It was for many years, and remains to some extent, the practice in the tire curing art to counter the extreme forces created by the introduction of high pressure fluids interiorly of a tire located within mold sections positioned in a press by the use of heavy mechanical components in the design of tire curing presses. The most successful and commonly employed mechanical designs have included base and cross beam elements of heavy steel, with reinforcing designed to minimize the deflection produced by the forces and moments developed during pressure loading of the press. The closing of the mold sections effected by movement of the cross beam and the application of sufficient squeeze or closing force to maintain the mold sections closed during the curing operation was normally produced by toggle mechanisms consisting of bull gears and trunion mounting side links which are attached to the cross beam by second trunions. Further, large side plates have been employed to control the movement of the second trunions in selectively located cam slots therein to dictate the path and orientation of the cross beam involved in its travel between closed and opened positions of the press.
Besides the size and complexity of the drive mechanisms for conventional mechanical tire curing presses, the interrelation of the conventional components has resulted in presses of extremely large size and weight, particularly in curing presses which are designed to accommodate larger tire sizes. The size, weight, and complexity of mechanical tire curing presses also translates into very high manufacturing, transportation, and installation costs. Nor have conventional mechanical curing presses been designed in a manner to reduce operating costs as by providing additional insulating material or other modifications to reduce energy inefficiencies which were long tolerated in regard to tire curing presses.
While it has been recognized for some years that hydraulically actuated presses could provide some significant advantages as contrasted with conventional mechanical operation, particularly in the context of a simple vertically opening press, a number of serious deterrents have been encountered in efforts to develop fully acceptable hydraulically actuated tire curing presses. As a result, a great number of different hydraulic actuated tire curing presses have evolved, with the various types exhibiting different advantages and disadvantages. One type of hydraulic tire curing press has employed a generally rectangular frame with a cross beam carrying the upper mold sections being positioned therein and movable by hydraulic cylinders interposed between the top frame member and the cross beam mounting the upper mold sections. In some instances, the opening and closing of the mold and the mold clamping mechanisms have been effected by the same hydraulic actuation devices. In other instances, hydraulic cylinders are employed for vertically moving of the cross beam to open and close the mold while clamping pressure is provided by other hydraulic actuators. In presses of this type, it is common to employ interlocking elements associated with the upper and lower mold sections or elements associated therewith to effect a locking engagement precluding press opening in the event of hydraulic pressure failure and during the operating cycle. In this respect, a wide variety of bayonet-type locking mechanisms of varying complexity and expense have been developed. In this type of hydraulic press, there are normally a plurality of additional cylinders located for operation on the molds to effect the requisite squeeze pressure to withstand the internal pressures encountered during the tire curing operation. Numerous arrangements and operational features of squeeze cylinder assemblies have developed which involve normally a balancing of advantages and disadvantages.
In lieu of bayonet locking assemblies, in some instances, strain rod locking assemblies have been employed which effect a positive locking irrespective of possible failure of hydraulic pressure supply to the press during the curing operation.
In other instances, efforts have been made to eliminate a basic rectangular frame construction and suspend one or more mold sections from one or more upstanding beams with an upfold section lifting cylinders coupled with suitable locking means and separate hydraulic elements for applying squeeze forces to the mold sections. While attractive in the elimination of portions of a press frame, arrangements of this type may be subject to inaccuracies in regard to registration between the mold sections and the complexity of the elements necessary to effect the accuracies which are currently required in the industry.
While most of the operational requirements for a tire curing press can be achieved by a hydraulically actuated press design, it is difficult in many instances to solve some extent problems without reverting to the size, weight, and complexity considerations comparable to those encountered with conventional mechanical presses while still accommodating the disadvantages of a sophisticated hydraulically operated device in a rubber processing facility.